22 Although this problem（）many times,it was too difficult（

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22 Although this problem（）many times,it was too difficult（）
A has been explained；to understand
B was explained；to be understood
C is being explained；to be understood
D had been explained；to understand
1 把题目和选项都翻译一遍
2 说出正确选项
3 解释为什么.越详细越好.

主句过去时,many times用完成时,所以用过去完成时
English is easy/ hard/ difficult to learn.语法要求不能变动,所以D

22 Although this problem（）many times,it was too difficult（ The maths problem was too difficult.____worked it out. 英语填空题 Although the problem was difficult,he solved it s_____ This math problem is too difficult _____.A.for me to work it This problem is too difficult.I can't work it out,and() This physics problem is too difficult for us to A work it ou This problem is too difficult._____ students can work it out This problem is too difficult.I can't work it out,and(). It is difficult () out this maths problem 单项选择（）1.----This physics problem is too difficult .Can you （）1.----This physics problem is too difficult .Can you show This problem is too difficult.Can you show me ______________

22 Although this problem（ ）many times,it was too difficult（

22 Although this problem（）many times,it was too difficult（